1. Field Of The Invention
The present invention relates to an apparatus for detecting a purification factor of a catalyst disposed in an exhaust system of an internal combustion engine for purifying an exhaust gas thereof.
2. Description Of The Related Art
As a conventional catalyst purification factor detecting apparatus, there is known an apparatus having such a structure that oxygen sensors are disposed at locations upstream and downstream of a catalyst, respectively, and the purification factor of the catalyst is detected on the basis of response delay times of the oxygen sensors (reference is made, for example, to U.S. Pat. No. 3,969,932).
The prior art apparatus suffers from such problems as mentioned below. The response delay time contains a response time of the oxygen sensor itself. This response time differs between respective oxygen sensors. Besides, the response time changes due to a change in the characteristics of the oxygen sensor caused by a change with time of the oxygen sensor. For these reasons, it is impossible or at least very difficult to detect the purification factor of a catalyst only on the basis of the response delay time with satisfactory accuracy.